Thermostatic control valve with fluid mixing

ABSTRACT

A thermostatic control valve assembly for use in continuously mixing a hot first fluid with a cold second fluid to continuously produce a mixed fluid at a constant temperature. The valve assembly includes an improved mixing dome defining a mixing chamber that facilitates thorough mixing of the hot and cold fluids over a wide range of flow rates, including rates as low as two gallons per minute. The improved mixing performance is accomplished by a plurality of baffles sequentially disposed along the flow path within the mixing chamber and extending at an angle in opposition to the flow path. Each baffle exhibits a paisley shape and is angularly displaced from the adjacent baffles to turn the fluid flow, thereby optimally mixing the hot and cold fluids over a wide range of flow rates while minimizing the pressure drop between the valve inlet and outlet.

This is a divisional patent application based on and claiming priorityto U.S. patent application Ser. No. 09/999,8 10, filed on Oct. 24, 2001,which issued on Oct. 28, 2003, as U.S. Pat. No. 6,637,668.

BACKGROUND OF THE INVENTION

The present invention relates to the field of fluid mixing valveassemblies. More particularly, the invention concerns an improvedthermostatically controlled mixing valve assembly in which a thermostatis immersed in the fluid flowing through the valve.

Thermostatic control valve assemblies are well known in the art and havelong been utilized in various applications including group showers,washing stations, hospital hydrotherapy installations and in manyindustrial applications where precision thermostatic water blending isessential. In order to operate properly, the hot and cold water enteringsuch a valve assembly must be thoroughly blended before the temperatureof the mixture is sensed by the thermostat. If the hot and cold waterare not adequately mixed, the valve assembly can behave erraticallybecause the temperature sensor sees pockets of hot and cold waterinstead of a mixture that is at a single temperature throughout. Oneproblem that has long persisted in the art is the inability of mostvalve assemblies to adequately mix the hot and cold water over a widerange of flow rates. Consequently, multiple valves often have to be usedto satisfy flow requirements.

Another problem that has persisted in the art is the physical size ofthe valve assembly required for a specific application. Often, the valveassembly is simply too large because of the need for a large mixingchamber to adequately mix the hot and cold water. What is needed is athermostatic control valve assembly having an improved mixing chamberthat has the ability to thoroughly mix the hot and cold water over awide range of flow rates, and which does so in a smaller physical spacethan valve assemblies currently known in the art.

One such valve assembly featuring an improved mixing chamber isdisclosed in U.S. Pat. No. 5,203,496 which is assigned to the assigneeof the present invention. It is now desired to improve the operation ofsuch valve assemblies by providing a mixing valve assembly whichoperates with reduced pressure drop across the valve assembly, whilestill thoroughly mixing the hot and cold fluids.

SUMMARY OF THE INVENTION

A thermostatic control valve assembly for continuously mixing a hotfirst fluid with a cold second fluid to continuously produce a mixedfluid at a constant temperature according to one embodiment of thepresent invention comprises a cold fluid inlet, a hot fluid inlet, amixing dome defining a mixing chamber, a thermostatically controlledflow control valve and an operably connected thermostat for adjustingthe flow of the hot and cold fluids into the mixing chamber. The mixingdome includes a plurality of baffles sequentially placed in the flowpath to promote better mixing of the hot and cold fluids before themixed fluid contacts the thermostat disposed in the fluid flow path.

In one aspect of the invention, each baffle projects into the flowstream and is angled from the mixing dome wall in a direction contraryto the direction of flow. The mixing performance is further improved byangularly displacing the each baffle with respect to each other toimpart a twisting movement to the fluid. The mixing dome includes meansfor supporting the thermostat between the baffles and the fluid outletof the dome.

A general object of the present invention is to provide an improvedthermostatic control valve assembly. A specific object is to provide avalve assembly that more efficiently mixes hot and cold fluids foraccurately sensing the temperature of the mixture.

A further objective is to provide a valve assembly that provideseffectively mixed hot and cold fluids with reduced pressure drop betweenthe valve and valve outlet. Related objects and advantages of thepresent invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side cross-sectional view of a thermostatic control valveassembly according to a preferred embodiment of the present invention.

FIG. 2 shows a side cross-sectional view of a housing defining animproved mixing chamber for the valve assembly shown in FIG. 1.

FIG. 3 is a top view along section 3—3 of FIG. 2 showing a first baffleaccording to the present invention.

FIG. 4 is a top view along section 4—4 of FIG. 2 showing a second baffleaccording to the present invention.

FIG. 5 is a top view along section 5—5 of FIG. 2 showing a third baffleaccording to the present invention.

FIG. 6 shows a side cross-sectional view of a housing defining animproved mixing chamber for a second embodiment of the presentinvention.

FIG. 7 is a top view along section 3—3 of FIG. 6 showing a first baffleaccording to the present invention.

FIG. 8 is a top view along section 4—4 of FIG. 6 showing a second baffleaccording to the present invention.

FIG. 9 is a top view along section 5—5 of FIG. 6 showing a third baffleaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring now to FIG. 1, there is shown a thermostatic control valveassembly 10 with fluid mixing according to the preferred embodiment ofthe present invention. Valve assembly 10 includes a hot inlet 11, a coldinlet 12 and an outlet 13. Inlets 11 and 12 are connected to oppositesides of flow control valve 14 and open to annular cavities 15 and 16,respectively, within the flow control valve. The inner wall of annularcavities 15 and 16 is defined by a cylindrically shaped liner 17. Liner17 is open at both ends and includes a plurality of openings or slots 18which are distributed around its circumference in communication withcavities 15 and 16.

Slidably mounted within liner 17 is a cylindrically shaped piston 19which is open at its upper end. Piston 19 is preferably pressurebalanced and includes a plurality of openings or slots 20 that aredistributed around its circumference. Preferably, each opening 20through piston 19 has a counterpart opening 18 in liner 17. Modulationof the piston 19 within the liner 17 variably opens the cavities 15 and16 to the interior of the piston 19, which communicates the combined hotand cold fluid to the outlet 14 a of the flow control valve.

Flow control valve 14 also includes a bottom plug 21 which can beremoved to allow access to repair, replace or clean the interior partsof flow control valve 14. Bottom plug 21 defines a cavity 22 thereinwhich substantially receives compressed valve spring 23. Valve spring 23is supported at one end by bottom plug 21 and is connected at its otherend to the base 24 of piston 19. The spring 23 applies a return force topiston 19.

A push rod 25 extends through the liner 17 and piston 19 to engage thebase 24. The opposite end of push rod 25 is connected to a thermostat26. Thermostat 26 can be of many types known in the art, such as athermal coil or a temperature sensitive bellows. Such a thermostat isdesigned to expand or contract along the axis defined by push rod 25 inlinear proportion to a change in the temperature of fluid surroundingthe thermostat. In this embodiment, thermostat 26 is connected toadjustment screw 27 via shaft 28. Adjustment screw 27 acts againstspring 23 and thus allows the vertical position of the thermostat 26,and ultimately of the piston 19, to be adjusted, which in turn altersthe relative proportions of hot and cold fluid passing through openings20.

One problem that has persisted in the art is the inability of valveassemblies to operate properly over a wide range of flow rates. In otherwords, a flow control valve assembly is only useful over the range offlow rates that the device is able to thoroughly blend the hot and coldfluids before the mixture contacts the thermostat. While many knownmixing valve assemblies are capable of adequate fluid mixing at highflows, a need remains for a valve assembly that is also capable ofthorough hot and cold fluid mixing at low flow rates, such as below 10g.p.m.

FIG. 1 illustrates one form of control valve assembly that may utilizethe features of the present invention. It is understood that theinvention can have application with a variety of thermostat controlvalve configurations. In the illustrated embodiment, a mixing dome 29 isengaged over the outlet 14 a of the flow control valve 14. The mixingdome 29 defines a mixing chamber 30 therein which is preferablycylindrical in configuration. An important feature of the presentinvention is the incorporation within the mixing dome 29 of means forturning or rotating the fluid flow through the mixing chamber 30 toensure complete mixing of the hot and cold fluid before it reaches thethermostat 26. Complete fluid mixing assures a uniform temperaturethroughout the fluid discharged through outlet 13. Most importantly, themixed fluid accurately reflects the exiting temperature of the fluid sothe thermostat can accurately regulate the movement of the valve controlelements.

According to the invention, the means for turning the fluid includes aplurality of baffles 31 that are integrally formed as part of thehousing 32 forming the mixing dome. The shape and relative arrangementof baffles 31 are intended to induce more thorough blending of the hotand cold fluids in mixing chamber 30 before the mixture contactsthermostat 26, particularly at low flow rates where the problem ofinadequate mixing is most prevalent.

In order to reliably react to a change in the temperature of the fluidmixture, the thermostat must be immersed in the mixture, and the mixturemust have a substantially uniform temperature throughout rather thanconsisting merely of hot and cold pockets. Baffles 31 of the presentinvention create a vortex in the fluid flow so that the hot and coldfluids remain in contact longer, leading to complete mixing resulting ina substantially uniform fluid mixture and temperature prior to flowingaround the immersed thermostat. In this manner, higher flow rates areachieved with only a minimal pressure drop between the valve inlet andoutlet.

The mixing dome 29 is shown in more detail in FIG. 2. The housing 32defines the mixing chamber 30 therein and a flow path 33 therethrough.The housing 32 is provided with a mating surface 35 and an annularflange 36 that enable the housing to be mated to flow control valve 14by conventional means. Housing 32 also defines an opening 37 at its topwhich permits an adjustment means, such as screw 27 and shaft 28, to beconnected to the thermostat, as better shown in FIG. 1. In operation,the fluid leaving flow control valve 14 enters housing 32 through inlet34. Immediately afterwards, the fluid encounters baffles 38, 39 and 40in successive order. The fluid mixture then continues upward along flowpath 33 until finally exiting housing 32 through outlet 13.

The outlet 13 is positioned at the end of the mixing chamber or fluidflow path to ensure that the thermostat 26 is substantially immersed inthe fluid exiting the valve assembly 10. Moreover, the thermostat 26 isdisposed downstream of the sequential baffles, preferably by a distancegreater than the distance between successive baffles. Thus, the hot andcold fluids are substantially mixed prior to the thermostat, andsubstantially all of the thermostat is exposed to the fluid mixture toassure that the thermostat receives a proper indication of thetemperature of the exiting fluid.

A more detailed view of each baffle is provided in the sectioned viewsof FIGS. 3, 4 and 5. Although not shown in FIG. 2, it should be notedthat if the vertical spacing of the baffles is sufficiently close, thebaffles will overlap so that a section taken through the housing willencompass more than one baffle. As best shown in FIG. 5, each baffle ispreferably curved in shape having a rounded first end 44 and a secondend 46 that tapers into the wall of the housing 32. The baffles runabout 210 degrees end to end. Each baffle is angled downward counter tothe direction of fluid flow, preferably at an angle of about 70 degreesas shown in FIG. 2. This arrangement imparts a turning action on thefluid stream, facilitating mixing of the hot and cold fluids. Thebaffles are most preferably arranged so that the tapered end 46 of thebaffles meet the fluid first. This minimizes turbulence and reducespressure drop as the fluid maintains laminar flow along the graduallywidening baffle. The housing 32 and baffles may be manufactured byconventional casting techniques, such as sand casting.

Each baffle is rotationally displaced from each adjacent baffle toproduce a helical arrangement of baffles 38, 39 and 40 in flow path 33.In this embodiment, each successive baffle is rotated through an angle48, which in the illustrated embodiment is 120 degrees, to produce agenerally helical flow path through the baffles. The helical pattern ofsuccessive baffles creates an overall amount of mixing which is greaterthan the sum of the individual baffles acting alone and withoutexcessive pressure drop.

In one specific embodiment of the invention, the housing 32 is ofsand-cast bronze and defines a cylindrical mixing chamber 2.0 inches indiameter and about 10.0 inches in length from the base of the mixingchamber to the center of the outlet opening 13. The baffles in thisspecific embodiment can be spaced about 1 inch apart. Each baffle canhave a maximum width of about ⅝ inches. Each baffle can have a totalsurface area that is about one-half the cross sectional area of thechamber.

Preferably, the baffles define an unobstructed center opening 49 alongthe subtended length of the housing. In a specific embodiment, thisopening 49 can have a diameter of ¾ inches for a 2 inch housing In amost preferred embodiment, the baffles assume a “paisely” shape tocreate the center opening and provide a smooth flow transition up eachbaffle. The valve assembly 10 of the specific embodiment is capable ofaccurately controlling the outlet fluid temperature at flows of 2–80g.p.m. The fluid mixing provided by the baffles is particularlyimportant at the low flow rates since the fluid flow can “short-circuit”the thermostat in which the entire thermostat is not immersed in thefluid flow prior to the outlet 13.

Another embodiment of the invention is shown the mixing dome 29 shown inFIG. 6. The housing 32 defines the mixing chamber 30 therein and a flowpath 33 therethrough as previously described.

A more detailed view of each baffle in this embodiment is provided inthe sectioned views of FIGS. 7, 8 and 9. Each baffle is crescent shapedand is angled downward counter to the direction of fluid flow,preferably at an angle of between 45 and 70 degrees. Again, the housing32 and baffles 38′, 39′, and 40′ may be manufactured by conventionalcasting techniques, such as sand casting.

Each baffle is rotationally displaced from each adjacent baffle toproduce a helical arrangement of baffles 38′, 39′ and 40′ in flow path33. In this embodiment, each successive baffle is rotated through anangle 48′, which in this case is about 45 degrees, to produce agenerally helical flow path through the baffles. Each baffle defines achord 41, 42, and 43 between its end points which is useful inillustrating the helical arrangement of the baffles in the flow path. InFIGS. 7–9, chords 42, 42, and 43 are show with their respectiveperpendicular bisectors successively rotated by an angle of about 45degrees. The helical pattern of successive baffles creates an overallamount of mixing which is greater than the sum of the individual bafflesacting alone and without excessive pressure drop.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

For instance, in the preferred embodiment, the baffles 38, 39 and 40 areintegrally formed in the housing 32 by known casting techniques. Theinvention further contemplates that each baffle constitutes a separateelement that is suitably mounted within a cylindrical cavity in thehousing. For instance, the separate baffles could be snap fitted withingrooves formed in the housing.

Moreover, the invention contemplates incorporating additional bafflessequentially disposed along the flow path. Multiple housing sections canbe combined, and more baffles can be added to the longer chamber. Theadditional baffles would preferably be arranged in the helical patterndescribed above. Thus, while the baffles of the preferred embodiment arerotated 120 degrees relative to each other, the addition of more bafflespermit smaller relative angular displacements between consecutivebaffles.

1. A mixing dome for use in a thermostatic control valve assembly havinga hot fluid inlet, a cold fluid inlet, a thermostatically controlledflow control valve combining the hot and cold fluid and a thermostatoperably coupled to control the flow control valve in response to thetemperature of the fluid mixture, the mixing dome comprising: a housinghaving an inner wall defining a mixing chamber in fluid communicationwith the hot and cold fluid inlets and the thermostat; and at least onebaffle affixed to said inner wall of said housing, said baffleincluding; a leading upstream surface portion tapered toward saidhousing; a trailing downstream surface portion wider than said upstreamsurface portion; and an arcuate edge portion connecting said upstreamand downstream surface portions.
 2. The mixing dome of claim 1 whereinsaid baffle runs about 210 degrees from said tapered upstream surfaceportion to said trailing downstream surface portion.
 3. The mixing domeof claim 1 wherein said baffle has a surface area that is about one-halfthe cross sectional area of the housing.
 4. The mixing dome of claim 1wherein said baffle has a paisley shape.
 5. The mixing dome of claim 1,wherein said at least one baffle includes two baffles sequentiallyarranged and angularly displaced along a length of said housing.
 6. Themixing dome of claim 5, wherein said two baffles are angularly displacedby an angle of about 120 degrees.
 7. The mixing dome of claim 5, whereinsaid at least one baffle includes a third baffle sequentially arrangedand angularly displaced from each of said two baffles along the lengthof said housing.
 8. A baffle for a mixing dome housing, said bafflecomprising: a leading upstream surface portion tapered toward thehousing; a trailing downstream surface portion wider than said upstreamsurface portion; and an arcuate edge portion connecting said upstreamand downstream surface portions.
 9. The baffle of claim 8 wherein saidbaffle runs about 210 degrees from said leading upstream surface portionto said trailing downstream surface portion.
 10. The baffle of claim 8wherein said baffle has a surface area that is about one-half the crosssectional area of the housing.
 11. The baffle of claim 8 wherein saidbaffle has a paisley shape.
 12. A baffle for a mixing dome housing, saidbaffle comprising: an upstream portion; a downstream portion; an outeredge arcuately extending from the upstream portion to the downstreamportion, the outer edge configured to be attached to the mixing domehousing; and an inner edge arcuately extending from the upstream portionto the downstream portion so as to define a concavity along the edge ofthe baffle, the inner edge on the side of the baffle opposite the outeredge; the baffle configured such that the distance between the inneredge and the outer edge at the upstream portion is a first distance andthe distance between the inner edge and the outer edge at the downstreamportion is a second distance, the second distance greater than the firstdistance.
 13. The baffle of claim 12, wherein said outer edge isconfigured such that when the baffle is attached to the mixing domehousing, the outer edge extends in an arc of about 210 degrees aroundthe inner surface of the mixing dome.
 14. The baffle of claim 12,further comprising: a first surface defined by the inner edge and theouter edge, the first surface having a surface area of about one-half ofthe cross-sectional area of the mixing dome housing.
 15. The baffle ofclaim 12, further comprising: a first surface defined by the inner edgeand the outer edge, wherein the first surface has a paisley shape whenthe baffle is attached to the mixing dome housing and the first surfaceis viewed from a point upstream of the upstream portion of the baffle.